The invention relates to a rotorcraft rotor in which the blades are, at least some of them, folding blades and equipped with an electric deicing or anti-icing device, entailing the routing of electrical energy to the blades from a collector placed at the centre of the hub of the rotor. This routing of electrical energy is performed using an electrical connection installation consisting essentially of an electric wiring harness and comprising, for each blade, at least one electric connecting cable connected to a member for connecting the corresponding blade to the hub of the rotor and equipped with connectors at its ends in order to make an electrical connection between the collector and the blade.
More specifically, the invention relates to a rotorcraft rotor, particularly a helicopter main rotor, of the type comprising:
a hub intended to be driven in rotation about an axis of the hub which is the axis of rotation of the rotor,
at least three blades, each of which is connected to the hub by a connecting member which is substantially radial with respect to the axis of rotation, and the outer radial end of which is shaped as a clevis in which the corresponding blade has its root retained by two blade pins each passing through aligned bores in the clevis and the blade root, the two blade pins being substantially mutually parallel, at least one blade being foldable on one side of the rotorcraft and having at least one removable blade pin, so that withdrawal of said removable blade pin from the blade root and from the clevis of the connecting member allows the blade to be pivoted about the other blade pin, and
an electrical connection installation comprising, for each blade, at least one electrical connecting cable connecting a first connector, carried by the hub and powered by at least one supply conductor, to a second connector mounted on the blade and connected to at least one electric conductor of an electric device for deicing or preventing the icing of said blade.
Rotorcraft rotors of this type are known, in particular, from EP 0 754 623 and FR 2 781 198.
For at least one folding blade of a rotor according to EP 0 754 623, the connecting cable comprises a first length, radially towards the outside, arranged as an overhead hook stretching from this blade to the corresponding connecting member and connecting the second connector on this blade to a first end, in an outer radial position, of a second length of connecting cable held substantially radially on this connecting member.
This overhead hook of the connecting cable has a rounded cross section, possibly a screened structure, and is connected to a plug of the second connector, which plug connects to a socket of this second connector, this socket being fixed to the blade and connected to the deicing conductor for this blade.
When a blade is folded, the pivotings of the blade root in the outer radial clevis of the corresponding connecting member may introduce damaging tension into the overhead hook and the second length of the connecting cable and into the second connector and/or this overhead hook may oppose the full folding of the blade.
To remedy this drawback, EP 0 754 623 makes provision for the plug of the second connector, on the corresponding end of the overhead hook of the connecting cable, to connect removably to the socket of the second connector, which is fixed to the blade. Giving this overhead hook a long enough length to allow the full folding of the blade without disconnecting the plug and socket of this connector is not advisable because an overhead hook of such a length would be subjected to significant forces and would undergo fairly high-amplitude whiplash movements encouraging it to catch unintentionally on nearby components, such as pendular blade root antivibrators or drag dampers, on a rotating rotor, the corresponding blade then making its angular excursions in pitch, flapping and drag.
If the blades are folded manually, it is therefore not possible to avoid manual disconnections and connections between the plug and the socket of the second connector, the former before folding and the latter after returning a blade to a flight configuration, if the advantages afforded by the other characteristics of the connection installation described in EP 0 754 623 are to be maintained.
By contrast, on a rotor whose blades can be folded xe2x80x9cautomaticallyxe2x80x9d, using actuators mounted on the connecting members, EP 0 754 623 proposes for the overhead hook between the blade and the connecting member to extend from the second connector, on the blade, to a rotating part of a rotary coupling, of which a stationary part, on the connecting member, is connected to the second length of cable held thereon, the rotating part of the rotary coupling being mounted to rotate coaxially with the pivoting connection between the blade and the connecting member so that the automatic foldings and unfoldings of the blade can be brought about without disconnections or connections having to be performed at either of the two connectors of the installation.
FR 2 781 198 proposes improvements to folding-blade rotors with the electric deicing installation according to EP 0 754 623, particularly in order to diminish the stresses and/or displacements of the connecting cable in its overhead hook length connecting the connecting member to the second connector on the blade when the rotor is turning and during operations of folding the blades back and forth.
To this end, according to FR 2 781 198, part of this overhead hook is held in at least one retaining member mounted in the substantially axial continuation of the folding axis. This technical step affords the following advantages: it is no longer necessary for the connection between the overhead hook and the deicing device to be disconnected at the second connector before the blade is folded and when this overhead hook is of a relatively short length. The retaining member thus prevents displacements of this overhead hook on each side of the folding axis, during the folding or unfolding of the blade, thus avoiding prejudicial twisting of this length of the connecting cable, provided that this overhead hook is long enough, and in order for this overhead hook of the connecting cable to itself adopt the position in which it is mechanically stressed the least, when a blade is being folded or unfolded, the retaining member can be mounted so that it swivels freely coaxially on the axis of folding.
Whether this rotating member is fixed or whether it swivels on the folding axis, it may be arranged as a fork in which an elongate part of this overhead hook, with a cross section substantially in the shape of a flattened rectangle, is engaged and held by at least one elastic tab.
However, the improvements proposed in FR 2 781 198 are not enough to avoid disconnections and connections between the connecting cable and the second connector on the blade during manual foldings and unfoldings of the blades when the foldings are performed using a manual folding device as described in EP 0 888 964.
What happens is that, to fold manually a folding blade, the two blade pins of which are removable, the device according to EP 0 888 964 comprises a removable spacer piece which spaces the root of the folding blade away from the corresponding connecting member, the spacer piece comprising a journal through which a first bore passes and a clevis with a second bore, the spacer piece being, once a first blade pin has been withdrawn and the blade has been pivoted with respect to the connecting member and about the second blade pin, able to be mounted in terms of rotation on the connecting member by the retaining of the spacer piece journal in the clevis of the connecting member using a pin (tooling) that can be engaged in the first spacer piece bore and in the bore, previously containing the first blade pin, of the clevis of the connecting member, and the spacer piece being capable of retaining the blade root in terms of rotation in the spacer piece clevis by engaging another pin in the second bore of the spacer piece and in the bore of the blade root which previously contained the first blade pin, so that, once the second blade pin has been withdrawn, the blade can be folded by pivoting its root in the spacer piece clevis and by pivoting the spacer piece via its journal in the clevis of the connecting member.
As described in EP 0 888 964, a folding device such as this with a removable spacer piece attached between the outer radial clevis of the connecting member and the root of the blade makes it possible to offset and also to incline the axis of pivoting of the folding blade, and therefore allows better control over the paths followed by the blades upon folding to prevent them from interfering with one another and with members associated with them, such as drag dampers, and also, in the folded position, to give them a more favourable position with respect to the fuselage and with respect to the tail boom of the helicopter and with respect to the wind.
However, as far as the deicing connecting cable is concerned, the drawback of such a folding device is that it is incompatible with a fixed-length electrical connection between the connector on the blade and the connector on the hub because this device moves the blade away from the connecting member and furthermore does not allow the use of members for retaining the overhead hook of the deicing connecting cables as proposed in FR 2 781 198, that is to say in the shape of forks, as mentioned previously, or in the shape of cylindrical casings coaxial with the axis of folding and consisting of two half-casings containing a length of at least one turn of this length of cable between the connecting member and the blade, an end part of this length passing through a half-casing secured to the bottom of the casing and fixed to this half-casing and a second end part of this length passing through the other half-casing which is mounted to rotate freely coaxially with the axis of folding on the half-casing of the bottom, fixed to the connecting member, as also described in FR 2 781 198.
The withdrawal of the blade pins and therefore of the retaining members they support, on the one hand, and the separation of the folding blade root from the connecting member, by the fitting of the spacer piece, on the other hand, mean that it is not possible to avoid disconnecting the connecting cable and the second connector in order to fold a blade equipped with a deicing connecting cable as described in EP 0 754 623 and FR 2 781 198, thus leaving the blade entirely free to move without the risk of pulling the second connector out.
However, this simple solution consisting in disconnecting the connecting cable from the second connector on the blade has two major drawbacks.
From the mechanical point of view, the repeated operations of connecting and disconnecting present high risks of quickly damaging the connection installation through premature wear of the second connector and/or by pulling out its connecting base fixed to the blade. These risks are exacerbated by the arduous operating conditions in which a connection/disconnection intervention has to be able to be performed, particularly poor weather conditions entailing the operators wearing thick gloves, and adopting uncomfortable positions, particularly when carrying out operations on a helicopter on board a ship.
From a purely operational point of view, the forgetting to disconnect the connecting cable from the second connector cannot be excluded, this leading to the socket of the latter or a connector support casing bonded to the blade being pulled out. In addition, this disconnection manipulation needed for folding a blade adds to the numerous other operations, particularly the fitting of the removable spacer piece for folding, and increases the complexity and total duration of the intervention during folding.
The problem underlying the invention is that of overcoming these drawbacks by avoiding disconnecting of the connecting cable and the second connector on the blade so that the latter can be folded, even when the rotor is equipped with a folding device with a removable spacer piece that is inserted between the blade root and the corresponding connecting member.
To this end, the rotorcraft rotor according to the invention, of the type set out hereinabove, is characterized in that the connecting cable for at least one folding blade comprises a first length connecting said second connector on said folding blade to a first end, in an outer radial position, of a second length, held on the corresponding connecting member of said connecting cable, said first length of which includes a part forming spare length and wound into an S-shape in a plane substantially perpendicular to the corresponding two blade pins around two reels each of which is mounted at the end of a respective one of the corresponding two blade pins so that withdrawal of at least one removable blade pin and of the corresponding reel releases at least a portion of said part forming spare length of said first length, allowing the blade to be folded back without disconnection at the second connector.
Thus the spare or excess length exhibited by the connecting cable between the second connector, on the blade, and the corresponding connecting member, is automatically released, at least partially, during the folding operation, allowing the blade to travel.
When the folding blade has both blade pins as removable pins and can be folded manually with the aid of a folding device of the type known from EP 0 888 964, with a removable spacer piece which spaces the blade root away from the corresponding connecting member, as explained hereinabove, it is clear that once the first blade pin and its reel have been withdrawn, to mount the spacer piece in terms of rotation on the connecting member using a tooling pin, and once the second blade pin and the corresponding reel have been withdrawn following the mounting of the blade root in terms of rotation in the spacer pin clevis by engaging another tooling pin, the blade can be folded by pivoting its root in the spacer piece clevis and by pivoting the spacer piece via its journal in the clevis of the connecting member, while the part forming spare length on the corresponding first length of the connecting cable is completely released by the aforementioned successive withdrawal of the two reels with the corresponding two blade pins.
Advantageously, to allow great deformations of the first length of the connecting cable during the blade-folding operation, this first length has, at least in its part forming spare length, a cross section which is substantially in the shape of a flattened rectangle, the largest dimension of which is substantially parallel to the blade pins, and therefore generally also to the axis of the rotor.
Such a first length of connecting cable advantageously collaborates with the corresponding second length when the latter, as known from EP 0 754 623 and FR 2 781 198, and for the reasons mentioned in those two documents, has an elongate part with a cross section substantially in the shape of a flattened rectangle, the largest dimension of which is directed substantially at right angles to the largest dimension of the substantially flattened rectangular cross section of the part forming spare length of the first length of cable, that is to say generally also substantially perpendicular to the axis of the rotor, particularly to make it easier for this second length of cable to be attached to the connecting member, to reduce aerodynamic drag and to lower the mechanical loadings exerted on this length of cable.
Advantageously, for a better connection between the first and second lengths of the connecting cable, this second length extends on the corresponding connecting member, in a direction that is inclined with respect to the longitudinal axis of this connecting member and in such a way that its first end, in an outer radial position, is laterally offset outwards, on the same side as that one of the two reels which has wrapped around it the portion of said part forming spare length to which said second length of connecting cable is connected.
Advantageously, to reduce the number of rotor parts and to make the blade pins and the reels easier to operate and to allow the part forming spare length to wind readily into an S-shape, each reel, of cylindrical overall external shape, is secured to a respective one of the two blade pins.
Advantageously in addition, each of the two reels has, at its end on the opposite side to the blade pin on which said reel is mounted, a rim projecting substantially radially towards the outside of said reel and which restrains said part forming spare length and wound in an S-shape, between the rims of the reels and the corresponding connecting member, against any displacement substantially parallel to the blade pins.
Thus, in the flight position, the part forming spare length of the first length of cable is held in place by the two reels which doubly restrain this length of cable, not only in the plane perpendicular to the blade pins, in which the S-shape of the part forming spare length prevents the radial and tangential deformations of this part of the first length of cable, but also in any plane parallel to the blade pins, in which this part of the first length of cable is held between the connecting member and said rim of the reels.
In addition, each reel is advantageously tubular and secured substantially coaxially to the corresponding blade pin, which is also tubular. Thus, each reel can accommodate the head of an elastic pin passing through the corresponding tubular blade pin to lock it in a position in which it retains the blade root in the clevis of the corresponding connecting member in the flight configuration.
Thus, the rotor according to the invention can also enjoy advantages resulting from the use of other particulars of the electric connection installation according to EP 0 754 623 and FR 2 781 198, to which reference can be made for further details, and the descriptions of which are incorporated into this description by way of reference.
In particular, the second length of the connecting cable may advantageously be connected to the first connector on the hub via a third length of the connecting cable, said third length comprising an overhead hook in the shape of a flattened half loop with a cross section substantially in the shape of a flattened rectangle the largest dimension of which is substantially perpendicular to the axis of rotation and the concave face of which faces substantially towards retaining and articulating means connecting the corresponding connecting member to the hub and substantially radially towards the axis of rotation, said overhead hook being thus deformable in terms of bending and in terms of torsion so as to accommodate angular excursions in terms of pitch, drag and flapping of the blade and of its connecting member for connecting it to the hub, as known from the aforementioned two documents.
Likewise, the second length of cable may advantageously be connected to the overhead hook of the third length of cable by a coupling connected to the connecting member by a connection which is articulated at least in terms of pivoting about an axis substantially parallel to the longitudinal (pitch-change) axis of the connecting member and of the blade, so as to lessen the mechanical stresses on the connecting cable while at the same time allowing loadings exerted on the latter when the rotor is rotating and when the corresponding blade is making angular excursions in terms of pitch, flapping and drag to be reacted correctly, as proposed in FR 2 781 198.